Thread tensioning device for sewing machines



United States Patent THREAD TENSIONING DEVICE FOR SEWING MACHINES Frederick F. Zeier, Stratfield, and Edward S. Skowronski,

Bridgeport, Comm, assignors to The Singer Manufacturing Company, Elizabeth, N. J., a corporation of New Jersey Application November 23, 1954, Serial No. 470,596

1 Claim. (Cl. 242-155) This invention relates to sewing machine thread tensioning devices, and more particularly, to drum-type thread tensioning devices wherein the thread is tensioned by engagement with a fric tionally braked rotatable drum.

It is an object to provide a device operative to impose a selected tension on a thread irrespective of the thread characteristics so that a wide variety of threads and a wide range of thread sizes may be accommodated, and so that a constant tension may be maintained despite the existence of irregularities in the diameter of the thread.

Another object is to provide a tension device of the above character with a novel combination of thread-guiding and tensioning instrumentalities arranged to provide optimum engagement of the thread with the threadengaging drum.

Still another object of this invention is to provide, in a thread tensioning device of the above character, friction brake members formed of nonmetallic material such as nylon and disposed in engagement with the thread-engaging drum to provide uniform frictional drag upon the drum.

With the above and other objects and advantages in view, as will hereinafter appear, the invention comprises the devices, combinations, and arrangements of parts hereinafter described and illustrated in the accompanying drawing of a preferred embodiment thereof, in which:

Fig. 1 represents a cross-sectional view taken substantially along the axis of the drum thread tensioning device of our invention;

Fig. 2 is a top plan view of the tensioning device having a portion of the friction brake broken away; and

Fig. 3 represents an enlarged view of the free extremity of the tension stud, partly in cross-section, taken substantially along line 3-3 of Fig. 2.

As is illustrated in the drawing, the rotatable threadengaging drum of this thread tensioning device is preferably provided in the form of a stamped sheet metal wheel formed at its center with a bearing aperture 11 through which extends a stud 12. Peripherally, the Wheel 10 is formed with a series of tooth-like radial extensions 13 bent alternately to opposite sides of the wheel to provide a flared rim for the reception of a loop of the thread to be tensioned. In Figs. 1 and 2, such a thread 2? is illustrated clearly as it passes through the tensioning device and into engagement between the alternately outturned teeth of the wheel 10. The thread path about the periphery of the wheel is slightly sinuous between the alternately outturned teeth and this has the advantage that a positive grip is provided between the thread and the wheel, serving to prevent the thread from slipping with respect to the Wheel.

The stud 12, upon which the wheel 10 is freely rotatable, is formed with an enlarged flange 14 and a threaded extremity 15 adapted to engage a threaded hole formed in a boss 16 on the sewing machine frame 17. At its free extremity, the stud 12 is split lengthwise by a slot 18 and formed with external threads 19.

Clamped between the machine frame boss 16 and the flange 14 of the stud 12, is a plate 28 formed with a slot 21 to accommodate the threaded extremity 1 5 of thestud. As is illustrated in Fig. 2, the plate preferably is formed with an elongated arm 22 provided with a series of threadguiding apertures 23 to facilitate the introduction of a thread from a supply to the thread tensioning device.

As best illustrated in Fig. 1, a pair of disk-like brake members 24-24 are provided, each being apertured loosely to embrace the stud 12. It has been found'that superior frictional characteristics will resultwith this drumtype tensioning device when the material for the brake members is of nylon. The brake members 24-24 are preferably made identicalin form, each with a smooth flat back 25 and with a face formed with a raised annular land 26. The brake members are disposed on the stud 12 in opposed relation, one at each side ofgthe thread-engaging Wheel 10. The back 25 of the innermost brake member is seated against the stud flange 14, and means are provided on the free extremity of the stud for biasing the brake members together with the lands 26-26 thereof in frictional engagement with the opposite sides of the threadengaging drum. To this end, an arched pressure plate 27 is arranged on the stud 12 against the flat back 25 of the outermost brake member. The pressure plate 27 is formed with a diameter bar or tongue 28 disposed to enter the slot 18 in the stud 12 to lock the plate against turning with respect to the stud. Slidably disposed on the stud is a first spring-guarding sleeve 29 having a flange 30 arranged to engage the pressure plate 27. A second spring-guarding sleeve 31 is slidably disposed on the stud 12 and is formed with an inturned tongue 32 adapted to enter the stud slot 18 to lock the sleeve against turning with respect to the stud. The second sleeve 31 is formed, nearest the free extremity of the stud, with a heavy flange 33 arranged to abut an adjusting nut 34 threaded on the stud 12. Disposed about the stud over each of the spring-guarding sleeves 29 and 31 and between the flanges 30 and 33 thereof is a coil spring 35. The pressure exerted by the coil spring 35 may be adjusted to provide the desired frictional resistance between the brake members 24-24 and the thread-engaging drum by merely turning the adjusting nut 34. In order to prevent accidental loosening of the adjusting nut, the abutting surfaces of both the adjusting nut 34 and of the flange 33 of the spring-guarding sleeve 31 are formed with intermeshing radially extending serrations 36.

One advantage attainable with the use of this drumtype thread tensioning device is that the thread can be consistently and evenly tensioned. By preventing the brake members from rotating, frictional resistance will be imposed upon the thread only by the action of the annular lands 26-26 of the brake members against the threadengaging drum 10, and the characteristics of the thread, therefore, will have no effect upon the tension imposed by this device.

In order that the brake members may be restrained from rotation with the thread-engaging wheel 10, the peripheral portion of each brake member is formed with a recess 37. As illustrated in Fig. 2, the recesses are preferably semicircular in form and are disposed to accommodate a stop member in the form of a pin 38 secured to the plate 20 and arranged to extend transversely across the brake members and adjacent to the periphery of the threadengaging drum 19. By means of the slot 21 in the plate 20, the position of the stop member may be adjusted until it is seated snugly in the recesses 37 of the brake members.

In addition to providing a stop member preventing rotation of the brake members, the pin 38 serves as a thread guide to direct the thread properly to and away from the thread-engaging drum. To this end, the pin 38 is formed preferably with a pair of thread-guiding eyelets 39 and 40 arranged substantially transversely one with respect to the other, and each opening at one side into the space between the brake members 2424. As illustrated in Fig. 2, the pin 38 is ideally located to directthe thread I by means of the eyelets 39 and 40 practically about the entire periphery of the thread-engaging drum 10. This substantially complete wrapping of the thread about the drum acts to prevent slippage of the thread with respect to the flared rim of the thread-engaging wheel 10 and thereby insures consistency of the tension which will be imposed upon the thread. 1

It is desirable in a sewing machine thread tensioning device that substantially the same tension be imposed upon the thread while it is moving through the tensioning device as imposed during those periods while the thread is not being drawn through. By the use of nylon brake members 2424, a substantially constant degree of tension is attained whether the thread is stationary in the tensioning device or is moving through the tensioning device atrany one of a wide range of speeds.

The thread tensioning device of this invention is designed to operate satisfactorily without lubricants of any description, however, lubricants are used extensively about commercial type sewing machines, and it is likely that lubricant will occasionally make its way into the thread tensioning device. When nylon braking members are used, the tension imposed upon the thread by the device of this invention will not be diminished in the event that lubricant does make its way to the surfaces of the brake memb ers and the thread-engaging drum that are in frictional engagement.

Having thus described the nature of the invention, what we claim herein is: p s

A thread-tensioning device for a sewing machine comprising a stud, a thread-engaging drum rotatable on said stud, a pair of nylon brake members disposed in spaced relation on said stud, one at each side of said thread-engag ing drum, means carried on said stud for biasing said brake members into frictional engagement one with each side of said thread-engaging drum, and a cylindrical stoppin fixed in substantially parallel relation to said stud and disposed in engagement with both of said brake members, said pin being formed with a pair of thread guiding eyelets arranged transversely with respect to each other and each opening into the space between said brake members so as to direct a thread to and away from said thread engaging drum.

References Cited in the file of this patent UNITED STATES PATENTS 413,657 Gibbs Oct. 29, 1889 626,175 Lofstedt May 30, 1899 2,681,772 Charney June 22, 1954 

